1. Field of the Invention
The invention relates to a composite material, to its use as lubricating metal coating and to a process for its preparation.
2. Description of the Related Art
Use is made, in numerous industrial fields, such as, for example, transportation, the connector industry or the armaments industry, of mechanical assemblies in which components in contact are in movement with respect to one another. In numerous cases, it is desirable to treat the surfaces of the components in contact in order to confer thereon, in addition to their fundamental properties, lubricating properties which are stable toward high temperatures, in order to increase the lifetime and the reliability of the mechanical assemblies in which the surfaces are in contact.
It is known to deposit lubricating composite coatings by electrolytic processes, either by the chemical route (electroless process) or by the electrochemical route. An “electroless” process for codeposition on a substrate is a process consisting in incorporating particles during the process of growth of a metal or of an alloy by catalyzed oxidation/reduction. A process for codeposition by the electrochemical route consists in incorporating particles during the process of growth of a metal or of an alloy on a substrate to be coated, starting from an electrolyte in an electrolysis cell.
For example, the deposition of a lubricating coating of PTFE in a nickel-based metal matrix by an “electroless” process starting from a suspension of a PTFE in a solution of nickel precursor is known from X. Hu et al. (Plating and Surface Finishing, March 1997). However, the coatings of this nature are unstable, the PTFE being destroyed at temperatures of greater than 300° C.
The preparation of NiP antifriction deposited layers incorporating inorganic fullerene-WS2 nanoparticles by an “electroless” process is described in particular by W. X. Chen et al. [Advanced Engineering Materials, vol. 4, No. 9, September 2002]. It is also possible to deposit NiP—B4C lubricating coatings by the “electroless” technique [cf. J. P. Ge et al., Plating and Surface Finishing, October 1998].
In addition, Ni—BNh coatings are described by M. Pushpavanam et al. [Metal Finishing, June 1995] and composite coatings formed of nickel charged with MoS2 are described by Yu-Chi Chang et al. [Electrochimica Acta, vol. 43, Issues 3-4, 1998, pp. 315-324]. In both cases, the coatings can be obtained by the electro-chemical route. However, boron nitrides have very low chemical resistances in acidic and basic media.